JL posted a couple of circuit suggestions in the "slow fade-in circuit" thread that used protected MOSFETs. (*) We've had a few discussions about those gizmos in this very boutique. I've actually never used one, but IIRC the wisdom has been that they're not nearly as robust as their makers claim. It's been awhile, though--anybody have recent experience with them, favourite parts and so on? Cheers Phil Hobbs (*) I'm trying to break myself of the habit of starting tangential discussions far down existing threads, which is why this new one. We need more engineering round here. -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Protected MOSFETs
Started by ●September 26, 2020
Reply by ●September 26, 20202020-09-26
Phil Hobbs wrote:> It's been awhile, though--anybody have recent experience with them, > favourite parts and so on?I was using the VND14NV04 to switch rectified AC 12V RMS (just the bridge, no filter cap). In a 100 channel lab device, there were 4 failures over 5 years. Interestingly, the failure mode has always been half-open. No data from purely DC applications, it was enough for me to send them to the trashcan. I have good experience with the IPS161, although it is not exactly what you are asking, but IMHO close enough to mention it. Best regards, Piotr
Reply by ●September 26, 20202020-09-26
On Sat, 26 Sep 2020 02:48:10 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>JL posted a couple of circuit suggestions in the "slow fade-in circuit" >thread that used protected MOSFETs. (*) > >We've had a few discussions about those gizmos in this very boutique. >I've actually never used one, but IIRC the wisdom has been that they're >not nearly as robust as their makers claim. > >It's been awhile, though--anybody have recent experience with them, >favourite parts and so on? > >Cheers > >Phil Hobbs > >(*) I'm trying to break myself of the habit of starting tangential >discussions far down existing threads, which is why this new one. We >need more engineering round here.I was thinking about a protected-gate mosfet, which is pretty common these days. They basically have a roughly 40 volt symmetric zener from gate to source. That's nice. I tried three of the claimed really protected mosfets, the ones with current and thermal limits. The ones that I tried were terrible. One didn't really protect itself. One oscillated horribly. Something else was nasty about the third. They seem to power their protection circuits from the gate drive, which means that you wind up doing half the work. If you find a good one, let us know. Lately I've been putting some power parts on a PCB copper pour with a shutdown thermistor incorporated into the MAX809 powerup reset circuit. Seems to work. You can do fun stuff around a MAX809. We need a MAX809 sort of thing that has a temperature shutdown built in. May exist. Isolated tab would be good. Zetex makes a SOT23 nickel RTD with isolation. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●September 26, 20202020-09-26
On 9/26/2020 1:48 AM, Phil Hobbs wrote:> JL posted a couple of circuit suggestions in the "slow fade-in circuit" > thread that used protected MOSFETs. (*) > > We've had a few discussions about those gizmos in this very boutique. > I've actually never used one, but IIRC the wisdom has been that they're > not nearly as robust as their makers claim. > > It's been awhile, though--anybody have recent experience with them, > favourite parts and so on? > > Cheers > > Phil Hobbs > > (*) I'm trying to break myself of the habit of starting tangential > discussions far down existing threads, which is why this new one. We > need more engineering round here. >This is disturbing. We have a few thousand of the NCV8402STT1G protected FET out and in use over the last couple of years. They are used as a uC interface to drive 20-40 feet or so of wires in customers' construction warning signs to operate running time meters (100mA) and some logic lines <10MA. We have had no failures so far, but I have never bench tested them and cannot testify as to their robustness. No failures does not mean there will be none in the future.
Reply by ●September 26, 20202020-09-26
On 2020-09-26 11:13, jlarkin@highlandsniptechnology.com wrote:> On Sat, 26 Sep 2020 02:48:10 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> JL posted a couple of circuit suggestions in the "slow fade-in circuit" >> thread that used protected MOSFETs. (*) >> >> We've had a few discussions about those gizmos in this very boutique. >> I've actually never used one, but IIRC the wisdom has been that they're >> not nearly as robust as their makers claim. >> >> It's been awhile, though--anybody have recent experience with them, >> favourite parts and so on? >> >> Cheers >> >> Phil Hobbs >> >> (*) I'm trying to break myself of the habit of starting tangential >> discussions far down existing threads, which is why this new one. We >> need more engineering round here. > > I was thinking about a protected-gate mosfet, which is pretty common > these days. They basically have a roughly 40 volt symmetric zener from > gate to source. That's nice. > > I tried three of the claimed really protected mosfets, the ones with > current and thermal limits. The ones that I tried were terrible. One > didn't really protect itself. One oscillated horribly. Something else > was nasty about the third. > > They seem to power their protection circuits from the gate drive, > which means that you wind up doing half the work. > > If you find a good one, let us know.Those are the ones I was talking about.> > Lately I've been putting some power parts on a PCB copper pour with a > shutdown thermistor incorporated into the MAX809 powerup reset > circuit. Seems to work.Not a bad idea. I usually use LM393s for that, but in situations where you need a POR anyway, dorking a MAX809 might be a win.> > You can do fun stuff around a MAX809. > > We need a MAX809 sort of thing that has a temperature shutdown built > in. May exist. Isolated tab would be good.MIC280 looks nice--settable local plus remote temperature measurement and thermal alarm, SMBus. I've never used it. Seems to be the only game in town, but doesn't have an externally-accessible POR function.> > Zetex makes a SOT23 nickel RTD with isolation.Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 26, 20202020-09-26
lørdag den 26. september 2020 kl. 17.14.13 UTC+2 skrev jla...@highlandsniptechnology.com:> On Sat, 26 Sep 2020 02:48:10 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >JL posted a couple of circuit suggestions in the "slow fade-in circuit" > >thread that used protected MOSFETs. (*) > > > >We've had a few discussions about those gizmos in this very boutique. > >I've actually never used one, but IIRC the wisdom has been that they're > >not nearly as robust as their makers claim. > > > >It's been awhile, though--anybody have recent experience with them, > >favourite parts and so on? > > > >Cheers > > > >Phil Hobbs > > > >(*) I'm trying to break myself of the habit of starting tangential > >discussions far down existing threads, which is why this new one. We > >need more engineering round here. > > I was thinking about a protected-gate mosfet, which is pretty common > these days. They basically have a roughly 40 volt symmetric zener from > gate to source. That's nice. > > I tried three of the claimed really protected mosfets, the ones with > current and thermal limits. The ones that I tried were terrible. One > didn't really protect itself. One oscillated horribly. Something else > was nasty about the third.which ones and what did you try? other than one type from Onsemi some 10 years ago I've not heard of any issues> > They seem to power their protection circuits from the gate drive, > which means that you wind up doing half the work.usually ~1mA gate drive and a series resistor how is that half the work?
Reply by ●September 27, 20202020-09-27
On Saturday, September 26, 2020 at 11:14:13 AM UTC-4, jla...@highlandsniptechnology.com wrote:> On Sat, 26 Sep 2020 02:48:10 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >JL posted a couple of circuit suggestions in the "slow fade-in circuit" > >thread that used protected MOSFETs. (*) > > > >We've had a few discussions about those gizmos in this very boutique. > >I've actually never used one, but IIRC the wisdom has been that they're > >not nearly as robust as their makers claim. > > > >It's been awhile, though--anybody have recent experience with them, > >favourite parts and so on? > > > >Cheers > > > >Phil Hobbs > > > >(*) I'm trying to break myself of the habit of starting tangential > >discussions far down existing threads, which is why this new one. We > >need more engineering round here. > > I was thinking about a protected-gate mosfet, which is pretty common > these days. They basically have a roughly 40 volt symmetric zener from > gate to source. That's nice. > > I tried three of the claimed really protected mosfets, the ones with > current and thermal limits. The ones that I tried were terrible. One > didn't really protect itself. One oscillated horribly. Something else > was nasty about the third.Right, I tested a few of these for a simple heater (I was mostly interested in the thermal limit) and none of them were as robust as I wanted. Nothing like thermally protected bjt parts (lm317, lm395) George H.> > They seem to power their protection circuits from the gate drive, > which means that you wind up doing half the work. > > If you find a good one, let us know. > > Lately I've been putting some power parts on a PCB copper pour with a > shutdown thermistor incorporated into the MAX809 powerup reset > circuit. Seems to work. > > You can do fun stuff around a MAX809. > > We need a MAX809 sort of thing that has a temperature shutdown built > in. May exist. Isolated tab would be good. > > Zetex makes a SOT23 nickel RTD with isolation. > > > > > > > > > > -- > > John Larkin Highland Technology, Inc > > Science teaches us to doubt. > > Claude Bernard
